1. Field Of The Invention
This invention relates to a technique for stabilizing 1,1,1-trichloroethane against vapor or liquid phase decomposition caused by contact with metallic iron.
2. Description Of Prior Art
1,1,1-TRICHLOROETHANE IS KNOWN TO BE A SUPERIOR SOLVENT FOR GREASE, OILS, TARS AND WAXES AND IT IS KNOWN TO BE GENERALLY NON-FLAMMABLE AND LESS POISONOUS THAN OTHER CHLORINATED HYDROCARBONS. Because of these desirable properties, 1,1,1-trichloroethane is frequently used as a grease-removing solvent for a variety of light and heavy metals. Its full industrial acceptance, however, has been somewhat limited, since it is easily decomposable when in contact with certain metals, and tends to generate corrosive amounts of hydrogen chloride. This decomposition reaction can occur even when the solvent is used as a cold liquid, although the reaction is more likely to occur at higher temperatures and especially in the hot vapor phase. This high tendency to decompose in the hot vapor phase has recently become an increasingly severe detriment, in view of the greater industrial use of vapor cleaning techniques for hot processing equipment.
Many stabilizers and stabilizing systems have been suggested to alleviate the extent of decomposition. It has been found, however, that the nature and degree of the decomposition reaction is dependent upon the particular metal being contacted. Stabilization of 1,1,1-trichloroethane against exposure to one type of metal will not necessarily be effective against exposure to a different metal. In fact, a stabilizer for contact with one metal, may actually act as an accelerator for decomposition when contacted with another metal.
A need exists, therefore, for a stabilizer or stabilizer system which is effective against decomposition caused by contact with a variety of different metals.
Iron is one of the several metals which is frequently in contact with 1,1,1-trichloroethane, since iron is frequently used as an element in forming anti-corrosion processing equipment.
It would be desirable, therefore, to provide a stabilizer or stabilizer system which is particularly effective for stabilization against decomposition initiated by iron.
There have been several disclosures of stabilizing systems for stabilization of various halogenated hydrocarbons, particularly methyl chloroform. It is well recognized in the art, however, that good stabilization of one type of halogenated hydrocarbon is no indication of successful stabilization against other halogenated hydrocarbons, since the nature and degree of the decomposition reaction is greatly different for each of the different halogenated hydrocarbons. For instance, the Brown reference, U.S. Pat. No. 3,049,571, discloses that methyl chloroform can be stabilized against vapor phase decomposition caused by contact with zinc by the combination of nitromethane, s-butyl alcohol, 1,4-dioxane, or monohydric acetylenic alcohol with a vicinal, aliphatic epoxide. Brown, however, does not disclose the problems inherent in the stabilization of 1,1,1-trichloroethane against contact with iron, and Brown specially indicates recognition of the well-known fact that special problems exist with methyl chloroform which do not exist with other chlorinated solvents.
The Cormany, et al, U.S. Pat. Nos. 3,265,747 and 3,251,891, each disclose that methyl chloroform can be stabilized against vapor phase decomposition caused by contact with a light metal such as aluminum, magnesium or their alloys, by the use of one or more stabilizers selected from a list of several hundred possible stabilizers, which include selected aliphatic and aromatic epoxides, such as styrene oxide. Cormany, et al, however, do not disclose the problems inherent in the stabilization of 1,1,1-trichloroethane against contact with iron and likewise specifically indicate that methyl chloroform presents its own unique difficulties regarding stabilization so that experiences in the stabilization of other halogenated hydrocarbons are not applicable.
The Campbell, et al reference, U.S. Pat. No. 3,661,788, discloses that methyl chloroform can be stabilized against decomposition initiated by iron by stabilizing amounts of pyran type compounds or mixtures thereof with auxiliary stabilizers such as various epoxides including aliphatic epoxides containing 3 - 6 carbon atoms. However, the stabilizing combinations of Campbell, et al differ from those of the present invention and do not stabilize methyl chloroform against iron as effectively as the stabilizing combination of the present invention.
A need exists, therefore, for a stabilization system for 1,1,1-trichloroethane against iron-initiated decomposition.